The present invention relates to rotary drill bits for drilling boreholes into subterranean formations. More particulary, the invention relates to a novel rotary bit design utilizing diamond cutting elements.
Drill bits utilizing diamonds or similar hard cutting elements are commonly employed in drilling and coring operations, particularly in hard subterranean formations such as chert, quartzitic sandstones or the like. The construction of such diamond drill bits usually includes a body portion having means for interconnection of the bit onto a drill string, and a matrix portion for mounting the diamonds or other cutting elements. Drilling fluid is directed down to the bottom of the borehole through the drill string and from a port generally disposed in the central portion of the bit. Fluid passageways or water courses that cross the drilling surfaces of the bit are also provided to transport this drilling fluid across the bit face to cool and lubricate the drilling surface of the bit and to facilitate movement of drill cuttings from the drilling area.
The general theory of diamond bit operation is not simply to crush the formation and thereby make drilling progress, but rather to create tiny fractures as the cutting elements pass over the formation so that drilling fluid which is maintained at a higher pressure than the formation pressure, can enter these fractures and remove the fractured portions of the formation. While most diamond bits use this crushing or fracturing action to create the hole, some bits have been developed which utilize a shearing action to cut through the formation.
Many different types of "diamond" cutting elements have been developed and used. These include natural diamonds, synthetic diamonds, and composites which include combinations of diamonds with other compounds such as tungsten carbide. Additionally, many different types of diamond shapes have been used. These include natural round stones, mechanically and chemically rounded and polished stones, natural cubic stones and natural octahedral stones. These stones have been inserted in many different configurations in diamond drill bits and in bits of many different shapes.
Although diamond drill bits are the best type of bit for hard formations, their penetration rate is lower than other types of bits since they generally have to rely on crushing and fracturing action to cut through the formation. Accordingly, it would be a significant advancement in the art to provide a diamond drill bit which retains the advantages of having the hard diamonds as the cutting elements while providing a means for increasing the penetration rate of the bit. Such a bit is disclosed and claimed herein.